Defoamers, antifoaming agents, and air release agents are chemical processing aids employed to minimize or eliminate foam in industrial operations. While the terms are often used interchangeably, they employ different mechanisms, so it is worth distinguishing between them.

  • Defoamers are foam control agents which are added to a system to reduce or eliminate foam after it has been formed.
  • Antifoaming agents are foam control agents which are added to a system or formulation to prevent the appearance or emergence of foam.
  • Air release agents help remove entrained gases from a solution and raise them to the surface.

These categories are not strictly mutually exclusive. For instance, many chemical formulations both prevent and destroy foam, in which case they could be classified both as antifoaming agents and defoamers. Additionally, many defoamers have some effect on entrained air, while some air release agents initiate the destabilization process for surface foam.

For the sake of simplicity, the term “defoamer” is generically used as an industry standard when referencing any processing aid designed to control foam.

What Is Foam?

Foam occurs when gas is introduced into and stabilized within a solution. In pure liquids (e.g. water), foam is thermodynamically unstable, and any bubbles will rapidly rise to the surface and burst. Stabilization is only possible in solutions containing additional surface active components that create a surface tension gradient at the gas-liquid interface (the foam lamella, foam film, or bubble wall), thereby allowing for much greater foam stability as air is introduced into the solution.

Gravity inherently drains the liquid from foam, which results in the formation of a “dry” polyhedral foam beginning from the top of the foam down. Individual bubbles vary in size and capillary pressure within the foam, so gas naturally diffuses from smaller, higher pressure bubbles to larger bubbles. However, as the foam film stretches, the concentration of surface active ingredients decreases. This decrease in concentration causes a local increase in the surface tension of the foam film, thereby impeding the coalescence of bubbles and stabilizing the foam (Gibbs-Marangoni Effect).

Foamkill Intro Bubbles